Animated oil spill on ocean surface
Final



Maybe something like this will be enough for you. It is fairly simple and made only with nodes. Rendered in EEVEE.

Overview

Ocean

It's a simple Plane with Ocean modifier and animated Time value. From 1 to 5 trough 150 frames.



Material

I've used "two parts" material. First one is shrinking circle (distorted) and second is main distortion. At the end of the node setup I've used Color Ramp to select ocean and oil colors. 

Shrinking is made by animating Mapping Scale.